1. Field of Invention
The present invention relates to a novel latent curing agent which reacts to heat and/or UV-light, an epoxy composition containing it, a mixed epoxy composition (blend) having different functional groups and improved mechanical properties, and cured epoxy products.
2. Background of Invention
The conventional epoxy curing systems adopted either amine-type curing agents which exhibit low heat resistance and are harmful to both the human body and the environment or anhydride-type curing agents which in order to be cured, require both large amounts of curing agents and a long time and also react with lower rates of efficiency. Such conventional epoxy curing systems result in high production costs, a deterioration of physical properties and contribute to environmental pollution problems. At present, leaders of advanced electric, electronic and automobile industries require the development of latent curing agents in order to firstly, avoid the problems of amine-type or anhydride-type curing agents, and secondly, to induce curing reaction at a relatively low temperature around 100xc2x0 C. within a time of between 30 and 120 minutes respectively and thirdly, to keep a storage period of more than six months whilst in a mixed state. The latent curing agents are specifically designed materials in order to allow the curing reaction initiated by heat, light, moisture or pressure, and are thus characterized by exhibiting control over the initiation stage.
Examples of typical latent curing agents in the cationic polymerization of epoxy resin include aromatic onium salts, which contain non-nucleophilic anions such as PF6xe2x88x92, SbF6xe2x88x92, AsF6xe2x88x92 and BF4xe2x88x92. However, certain problem with such aromatic onium salts containing non-nucleophilic anions used before now include a limitation in their solvent selectivity and also a large shrinkage after curing reaction and toxicity when they are used as latent initiators for epoxy resins.
Furthermore, the conventional epoxy resins exhibit relatively low heat and oxidation resistance properties in comparison to other high heat resistant resins, regardless of either their good electric insulating properties, processability, chemical resistance or mechanical strength. It is for these reasons that the applicability of such conventional epoxy resins has been restricted.
It is, therefore, an objective of the present invention to develop a curing agent, which possesses the following advantages:
the curing agent is able to overcome the associated problems of conventional amine-type or anhydride-type curing agents including high production costs, the deterioration of physical properties, the contribution to environmental pollution, and the long curing time required for the curing of epoxy resins;
the curing agent possesses latency properties capable of initiating a curing reaction not only by heat but also by light, such as UV-light, when used in small amounts under the correct reaction conditions;
the curing agent can accelerate a curing reaction both at a relatively low temperature of approximately 100xc2x0 C. and also within a short time frame; and
the curing agent has a storage period of more than several months whilst in a mixed state.
Another objective of the present invention is to provide an epoxy resin composition with significantly improved physical properties in comparison to the conventional epoxy resins, by the blending of epoxy resins containing different functional groups.
A further objective of the present invention is to allow the manufacture of cured epoxy products by means of heat or UV-light or both heat and UV-light.
The other objectives and features of the present invention will become apparent to those skilled in the art on review of the following detailed description. It should be understood, however, that the detailed description and specific examples, whilst indicating preferred embodiments of the present invention, are given by way of illustration and not limitation. Many changes and modifications within the scope of the present invention may be made without departing from the spirit thereof, and the invention includes all such modifications.